1. Field of the Invention
The present invention relates to a catalyst for the removal or elimination of hydrogen from an atmosphere containing hydrogen, oxygen and steam. The catalyst consists of a metal or a corresponding alloy which influences the oxidation of the hydrogen, and which is applied onto a substrate material as a catalyst layer.
The elimination or removal of hydrogen from a gas mixture which contains hydrogen and oxygen and, resultingly, is explosive in nature, is of particular significance to nuclear power plant accidents. Above all, such gas mixtures can be encountered during core melt-down accidents of light-water reactors, as well as in reactors which are modified to heavy water. Additionally, during the storage or; final storage of the burned-down fuel rods, hydrogen and its isotopes which are present in the enclosed oxygen-containing atmosphere, are released thereby and carry along a certain potential for danger.
2. Discussion of the Prior Art
In the disclosure of copending U.S. patent application Ser. No. 225,009, commonly assigned to the assignees of the present application, there are described catalyst layers which are constituted from PdNiCu alloys. It has evidenced itself that such catalysts constituted from Pd, Ni, Cu as well as PdAg or PdCu which are applied onto carrier or substrate materials exhibit a considerable potential for a utilization in the removal of hydrogen during accident situations connected with core melt-down. These alloys possess a good catalytic activity, even in the presence of toxic catalyst materials; for example, such as CO, J and S. The alloys evidence extremely short delay periods up to the commencement of a catalytic reaction.
In accordance with theoretical computations concerning the course of a core melt-down accident, there is to be expected that the release of the hydrogen will be related with the release of small quantities of CO.sub.2 and CO. Moreover, a considerable quantity of steam will be released during the accident. The steam is present in partially a sub-cooled and over a period of time in a super-heated condition. The release of the steam over time depends primarily upon the sequence of the accident. However, even at the same sequence for the accident will the steam content of steam be differently encountered in the different spatial or room divisions of the safety containment. It allows itself to be evidenced that the release of the steam must be considered from practically the beginning of the nuclear core melt-down accident. In accordance with the division of the spaces or chambers, the steam content will pass through different peaks over a period of time due to condensation and a varying release of steam. The steam content can reach in a chamber or containment of a security containment short-term values of from less than 20% up to 95%.
While there can be counted on the release of steam from the very beginning of the accident, the initial release of the hydrogen takes place, at a certain delay, after about one hour. The highest hydrogen concentrations are to be expected, especially after the failure of the reactor pressure container, within the first hours of the release thereof in the middle and lower installation chambers or spaces. Over the long-term, in the atmosphere of the security containment there can form themselves higher concentrations of ignitable gas mixtures, and upon a combustion of the hydrogen will endanger the safety containment.
An analysis of the different accident sequences leads to the conclusion that, with regard to such accident situations, there must be counted on the long-term release of steam. This signifies that the catalyst for the removal of hydrogen must also be exposed to a flow of steam over a lengthy period of time. Hereby, there must be considered that light-water reactors are operated with deionized water, which is particularly known for its corrosive capability.